Treating oil wells



' satisfactorily react acid salts .or soaps Patented Dec. 14, 1943 UNITE TREATING on. wan s Joe K. Butler and Samu Columbia, Tcx.,

cl A. Winkelmann, West assignors, by mesne assignments, to Leo Clark Morgan, Wichita, Kane.

- No Drawing. Application May Serial-No. 143,460

- 12 Claims. (01. tea-8.55)

This invention relates to the acid treatment of an oil well for. the purpose of'rendering the oil sands more permeable and increasing the flow therefrom. I r

In the acidizing of oil wells, such as with inhibited hydrochloric acid, it is found that certain oil-bearing-sands of high lime content will not quentlytrue; for example, of the Miocene sands throughout-the Gulf Coast area. Consequently, attempts to clean calcareous material off of the screen, and out of the pore-space in the sands by the useof acid have not proved satisfactory in numerous cases. oil about the, particles of the sand afford the calcite particles protection against reaction with the acid. Itls also believed that the poor results obtained from raw acid are due to the formation of acid oil gums, by reaction of the acid with the oil to produce a complex gummy material. Such gums or other precipitates which may be formed clog the pore space of the sand, and decrease the effective porosity and permeability.

i It is an object of the present invention to provide a method of acid treating an oil-bearing sand of this character so as to overcome the above noted objections, obtain an efiective reaction of the acid with the calcareous material, and substantially increase theporosity of the oil-bearing sand and thereby increase the oil flow.

We have discovered that the protective oil films about the sand particles may be effectively re moved by forcing into the cent sand a water solution of a chemical reagent which is efiective to cause the oil to be taken up by the water solution, probably in the form of an emulsion. Suitable chemical reagents of this type are the alkali metal salts or soaps of sulfonic and naphthenic acids. Other water soluble fatty may be used, particularly'the alkali metal'soaps of sulfonated fats and fatty acids. These include natural olein, stearin and the like, which have been sulfonated by treatment with sulfuric acid. Likewise, sulfonated fatty acids formed by sulfonating stearic, palmitic, oleic, and lower fatty acids such as acetic, propionic and the like, are included. A very satisfactory and comparatively cheap material is the sulfonic sludge acid derivedjrom the treating of petroleum oil with sulfuric acid.

Chemicals of the above character also lower the surface tension of the water, so that it penetrates the sand more easily. i a

In accordance with the present invention, an

with the acid. This is ire-- Apparently coatings or films of fats such as tallow,

the treatment of such sands with alkaline water solution of a soap of the character specified above is forced into the bore of the well and thence into the adjacent sand, to thereby remove the oil film from the sand particles. This is followed by flushing with water to remove the the oil taken up therefirst solution together with by, and to leave the sand particles exposed for effective contact with acid. Following this, a charge of inhibited acid, such as inhibited hydrochloric acid, is forced into the well where it performs its work effectively in-dissolving calcareous material and producing a solution of calcium employed. If the solution becomes acidic, a prewell and into the adja- Q cipitate is formed which will decrease the porosity of the sand. There is also incorporated with the oil-removing or emulsifying reagent an alkali metal hexametaphosphate, including such compounds as sodium hexametaphosphate, potassium hexametaphosphate, lithium hexametaphosphate, and ammonium,hexametaphosphate. The chem ical formula usually ascribed to the hexametaphosphates is exemplified by that for the sodium salt (NaPOaM. The latter is available commercially in a form which upon solution in water gives an alkaline reaction.

When one of the above metaphosphate compoundsiis combined with the water-soluble soap or oil-removing reagent, the latter is rendered immune to reaction with calcium and magnesium compounds which may be dissolved from the sand. If. such a metaphosphate were not present, and calcium and magnesium ions are formed in the water solution used to flush off the oil film, then these calcium and magnesium ions will react with the soap to form insoluble calcium and magnesium soaps which precipitate within the sand,

decreasing the porosity thereof. The hexametaphosphate has the property of segregating the calcium and magnesium ions in substantially non-ionized but water-soluble form. Although we are unable to give a theoretical explanation of this, we believe that the hexametaphosphate compound reacts, with the undesirable calcium and magnesium ions, forming complex compounds which are only slightly ionized but which remain 1 in water solution. The net result is that the oil film is efiectively removed from the sand, while at the same time precipitation of oil gums and water-insoluble compounds within the sand is avoided. The solution can then be flushed from the sand, which has thus been conditioned for the subsequent acid treatment.

As a specific example of our invention, a producing well was first treated with a mix consisting of 25 gallons of 18 B. hydrochloric acid (inhibited) and 25 gallons of fresh water to remove cem'ent obstruction from the screen, and open up the well and sand for subsequent treatment. This was immediately followed by pumping in 25 gallons of fresh waterto force out the preceding acid solution with contained reaction products. This was promptly followed by pumping in a solution prepared by dissolving in 3000 gallons of fresh water, the following con- This was followed by pumping in 300 gallons of stituents:

' Per cent 100# NaOH .0.4 62# sulfonic acid sludge 0.25 200# sodium hexametaphosphate 0.8

fresh water to flush out the previous solution.

Finally there was pumped in a mix consisting of 1000 gallons of 18 B. hydrochloric acid (inhibited) together with 1000 gallons of fresh water.

The above solutions or liquids are pumped into the sand as continuously as possible, so that one solution or liquid follows the other in close successlon into and through the oil-bearing sand adjacent the bore of the well. After all of the above solutions or liquids have been pumped into the well, the liquid remaining therein is allowed to remain about one hour to complete reaction, and then is removed by swabbing or In the example set forth above, the oil well was converted from one making gas only, but from which 011 would not flow, to one which produced 537 barrels of gross fluid per day, equivalent to 419 barrels of oil after deducting the to remove the oil film preceding the treatment with acid, substantial advantages are attained. A relatively clean calcareous sand is presented for reaction with the acid. Production of acid oil gumsand precipitation thereof in the sand are substantially avoided. The reaction of the hydrochloric acid with the calcium carbonate goes substantially to completion, and the solution of the water soluble calcium "chloride is washed ma a sand. The precipitation of insoluble calci or magnesium soaps within the sand is avoided by the selective action of the hexametaphosphate. The sand is made more permeable to oils by reason of the washing with the chemical mixture. 'Silicic acid which may be formed is washed out with the treating solution'and does not clog the pores. The pressure necessary for pumping the acid into the formation is reduced due to the increase impermeability after washing, with the chemical mixture.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are ppended claims. 1

We claim:

1. In the acid treatment of an oil well to increase the flow therefrom, the steps which comprise introducing into the well and the adjacent oil-bearing sand a solution of a chemical effective to remove the protective oil films from parindicated in .the

ticles of the sand, said solution also containing a metaphosphate effective to inhibit the formation of calcium and magnesium ions so as to avoid precipitation within the sand of insoluble calcium and magnesium compounds, and then introducing into the well and the adjacent oilbearing sand an acid to react with calcareous constituents of the formation from which the protective oil films have been removed.

2. In the acid treatment of an oil well to increase the flow therefrom, the step which comprises treating the well and the adjacent oilbearing sand to remove the protective oil fllms about the particles -of the sand prior to acid treatment thereof, with an alkaline water solution of an alkali metal soap and a hexametaphosphate.

3. In' the acid treatment of an oil well to increase the flow therefrom, the step which comprises treating the well and the adjacent oilbearing sand to remove the protective oil films about the particles of the sand prior to acid treatment thereof, with an alkaline water solution of an alkali metal soap of a sulfonated fatty acid and a hexametaphosphate.

4. In the acid treatment of an oil well to increase the flow therefrom, the step which comprises treating the well and the adjacent oilbearing sand to remove the protective oil films about the particles of the sand prior to acid treatment thereof, with an alkaline water solution of an alkali metal soap of a mineral oil sludge sulfonic acid and a hexametaphosphate.

5. In the acid treatment of an oil well to increase the flow therefrom, the step which comprises treating the well and the adjacent oilbearing sand to remove the protective oil films about the particles of the sand prior to acid treatment thereof, with an alkaline water solution of a water soluble emulsifying agent and analkali metal hexametaphosphate.

6. In the acid treatment of an oil well to in crease the flow ,therefrom, the step which comprises treating the well and the adjacent oilbearing sand to remove the protective oil films about the particles of the sand prior to acid treatment thereof, with a water solution prepared by dissolving therein acid sludge from the treatment of mineral oil with sulfuric acid, an excess of sodium hydroxide over that required to neutralize the sulfonic acids of the sludge and sodium hexametaphosphate.

7. The method of treating an oil well to increase the flow therefrom, which comprises introducing into the well and the adjacent oil-beam ing sand in the order stated an alkaline water solution of an alkali metal soap and a hexametaphosphate, flushing water, and inhibited hydrochloric acid.

8. The method of treating an oil well to increase the flow therefrom, which comprises introducing into the, well and the adjacent oilbearing sand in the order stated an alkaline water solution of an alkali metal soap of mineral oil sludge sulfonic acids and an alkali metal 9. The method oi' treating an oil well to increase the flow therefrom, which comprises introducing into the well and the adjacent oilbearing sand in the order stated, a comparatively small amount of inhibited acid, flushing water, an alkaline water solution of an alkali metal soap and an alkali metal hexametaphosphate,

flushing water, and the main quantity of in hibited acid, and then removing remaining liquid with contained reaction products from the well;

10. The method of treating an oil well to increase the flow therefrom, which comprises in-' to remove the protective oil films from the sand particles and an alkali metal hexametaphosphate, flushing water, and the main quantity of inhibited acid, and then removing remaining liquid with contained-reaction products from the well.

11. In the acid treatment of an oil well to increase the flow therefrom, the steps which comprise introducing into the well and the adiacent oil-bearing sand a solution of a chemical adapted to remove protective oil films from particles of the sand, said solution also containing a metaphosphate eflective to inhibit the formation of calcium and magnesium ions so as to avoid precipitation within the sand of insoluble calcium and magnesium compounds, then introducing flushing water into the well and the ad- Jacent oil-bearing sand. and thereafter an acid adapted to react with calcareous constituents of the. formation from which the protective oil films have been removed.

12. The method of treating an oil well to increase the flow therefrom which 'comprises introducing into the well and the adjacent oilbearing sand, an alkaline solution of a chemical eflective to remove the protective oil films from particles of the sand, said solution also containing a metaphosphate reflective to inhibit the formation of calcium and magnesium ions so as to avoid precipitation within the sand of insoluble calcium and magnesium compounds, then introducing flushing water into the well and the adjacent oil-hearing sand, and thereafter an acid to react with calcareous constituents of the formation from which the protective' oil fllms have been removed.

JOE K. BUTLER. SAMUEL A. WINKEIMANN. 

